Create BCLog::Level::Trace log severity level

for verbose log messages for development or debugging only, as bitcoind may run
more slowly, that are more granular/frequent than the Debug log level, i.e. for
very high-frequency, low-level messages to be logged distinctly from
higher-level, less-frequent debug logging that could still be usable in production.

An example would be to log higher-level peer events (connection, disconnection,
misbehavior, eviction) as Debug, versus Trace for low-level, high-volume p2p
messages in the BCLog::NET category. This will enable the user to log only the
former without the latter, in order to focus on high-level peer management events.

With respect to the name, "trace" is suggested as the most granular level
in resources like the following:
- https://sematext.com/blog/logging-levels
- https://howtodoinjava.com/log4j2/logging-levels

Update the test framework and add test coverage.

5 files changed, 18 insertions, 13 deletions

diff --git a/src/logging.cpp b/src/logging.cpp
index 0de74c4913..a609a021d1 100644
--- a/src/logging.cpp
+++ b/src/logging.cpp
@@ -202,6 +202,8 @@ bool GetLogCategory(BCLog::LogFlags& flag, const std::string& str)
 std::string BCLog::Logger::LogLevelToStr(BCLog::Level level) const
 {
     switch (level) {
+    case BCLog::Level::Trace:
+        return "trace";
     case BCLog::Level::Debug:
         return "debug";
     case BCLog::Level::Info:
@@ -286,7 +288,9 @@ std::string LogCategoryToStr(BCLog::LogFlags category)
 
 static std::optional<BCLog::Level> GetLogLevel(const std::string& level_str)
 {
-    if (level_str == "debug") {
+    if (level_str == "trace") {
+        return BCLog::Level::Trace;
+    } else if (level_str == "debug") {
         return BCLog::Level::Debug;
     } else if (level_str == "info") {
         return BCLog::Level::Info;
@@ -320,9 +324,9 @@ std::vector<LogCategory> BCLog::Logger::LogCategoriesList() const
 }
 
 /** Log severity levels that can be selected by the user. */
-static constexpr std::array<BCLog::Level, 2> LogLevelsList()
+static constexpr std::array<BCLog::Level, 3> LogLevelsList()
 {
-    return {BCLog::Level::Info, BCLog::Level::Debug};
+    return {BCLog::Level::Info, BCLog::Level::Debug, BCLog::Level::Trace};
 }
 
 std::string BCLog::Logger::LogLevelsString() const
diff --git a/src/logging.h b/src/logging.h
index 1288efa0fe..fe91ee43a5 100644
--- a/src/logging.h
+++ b/src/logging.h
@@ -69,7 +69,8 @@ namespace BCLog {
         ALL         = ~(uint32_t)0,
     };
     enum class Level {
-        Debug = 0, // High-volume or detailed logging for development/debugging
+        Trace = 0, // High-volume or detailed logging for development/debugging
+        Debug,     // Reasonably noisy logging, but still usable in production
         Info,      // Default
         Warning,
         Error,
diff --git a/src/test/i2p_tests.cpp b/src/test/i2p_tests.cpp
index 6fb104622d..43e4303ae3 100644
--- a/src/test/i2p_tests.cpp
+++ b/src/test/i2p_tests.cpp
@@ -21,7 +21,7 @@ BOOST_FIXTURE_TEST_SUITE(i2p_tests, BasicTestingSetup)
 BOOST_AUTO_TEST_CASE(unlimited_recv)
 {
     const auto prev_log_level{LogInstance().LogLevel()};
-    LogInstance().SetLogLevel(BCLog::Level::Debug);
+    LogInstance().SetLogLevel(BCLog::Level::Trace);
     auto CreateSockOrig = CreateSock;
 
     // Mock CreateSock() to create MockSock.
diff --git a/src/test/logging_tests.cpp b/src/test/logging_tests.cpp
index 352b517890..a6f3a62c71 100644
--- a/src/test/logging_tests.cpp
+++ b/src/test/logging_tests.cpp
@@ -172,18 +172,18 @@ BOOST_FIXTURE_TEST_CASE(logging_SeverityLevels, LogSetup)
 {
     LogInstance().EnableCategory(BCLog::LogFlags::ALL);
 
-    LogInstance().SetLogLevel(BCLog::Level::Info);
+    LogInstance().SetLogLevel(BCLog::Level::Debug);
     LogInstance().SetCategoryLogLevel(/*category_str=*/"net", /*level_str=*/"info");
 
     // Global log level
     LogPrintLevel(BCLog::HTTP, BCLog::Level::Info, "foo1: %s\n", "bar1");
-    LogPrintLevel(BCLog::MEMPOOL, BCLog::Level::Debug, "foo2: %s. This log level is lower than the global one.\n", "bar2");
+    LogPrintLevel(BCLog::MEMPOOL, BCLog::Level::Trace, "foo2: %s. This log level is lower than the global one.\n", "bar2");
     LogPrintLevel(BCLog::VALIDATION, BCLog::Level::Warning, "foo3: %s\n", "bar3");
     LogPrintLevel(BCLog::RPC, BCLog::Level::Error, "foo4: %s\n", "bar4");
 
     // Category-specific log level
     LogPrintLevel(BCLog::NET, BCLog::Level::Warning, "foo5: %s\n", "bar5");
-    LogPrintLevel(BCLog::NET, BCLog::Level::Debug, "foo6: %s. This log level is lower than the category-specific one.\n", "bar6");
+    LogPrintLevel(BCLog::NET, BCLog::Level::Debug, "foo6: %s. This log level is the same as the global one but lower than the category-specific one, which takes precedence. \n", "bar6");
     LogPrintLevel(BCLog::NET, BCLog::Level::Error, "foo7: %s\n", "bar7");
 
     std::vector<std::string> expected = {
@@ -220,7 +220,7 @@ BOOST_FIXTURE_TEST_CASE(logging_Conf, LogSetup)
         ResetLogger();
         ArgsManager args;
         args.AddArg("-loglevel", "...", ArgsManager::ALLOW_ANY, OptionsCategory::DEBUG_TEST);
-        const char* argv_test[] = {"bitcoind", "-loglevel=net:debug"};
+        const char* argv_test[] = {"bitcoind", "-loglevel=net:trace"};
         std::string err;
         BOOST_REQUIRE(args.ParseParameters(2, argv_test, err));
         init::SetLoggingLevel(args);
@@ -229,7 +229,7 @@ BOOST_FIXTURE_TEST_CASE(logging_Conf, LogSetup)
         const auto& category_levels{LogInstance().CategoryLevels()};
         const auto net_it{category_levels.find(BCLog::LogFlags::NET)};
         BOOST_REQUIRE(net_it != category_levels.end());
-        BOOST_CHECK_EQUAL(net_it->second, BCLog::Level::Debug);
+        BOOST_CHECK_EQUAL(net_it->second, BCLog::Level::Trace);
     }
 
     // Set both global log level and category-specific log level
@@ -237,7 +237,7 @@ BOOST_FIXTURE_TEST_CASE(logging_Conf, LogSetup)
         ResetLogger();
         ArgsManager args;
         args.AddArg("-loglevel", "...", ArgsManager::ALLOW_ANY, OptionsCategory::DEBUG_TEST);
-        const char* argv_test[] = {"bitcoind", "-loglevel=debug", "-loglevel=net:debug", "-loglevel=http:info"};
+        const char* argv_test[] = {"bitcoind", "-loglevel=debug", "-loglevel=net:trace", "-loglevel=http:info"};
         std::string err;
         BOOST_REQUIRE(args.ParseParameters(4, argv_test, err));
         init::SetLoggingLevel(args);
@@ -248,7 +248,7 @@ BOOST_FIXTURE_TEST_CASE(logging_Conf, LogSetup)
 
         const auto net_it{category_levels.find(BCLog::LogFlags::NET)};
         BOOST_CHECK(net_it != category_levels.end());
-        BOOST_CHECK_EQUAL(net_it->second, BCLog::Level::Debug);
+        BOOST_CHECK_EQUAL(net_it->second, BCLog::Level::Trace);
 
         const auto http_it{category_levels.find(BCLog::LogFlags::HTTP)};
         BOOST_CHECK(http_it != category_levels.end());
diff --git a/src/test/util/setup_common.cpp b/src/test/util/setup_common.cpp
index 872310f1ca..e8e96b9051 100644
--- a/src/test/util/setup_common.cpp
+++ b/src/test/util/setup_common.cpp
@@ -108,7 +108,7 @@ BasicTestingSetup::BasicTestingSetup(const std::string& chainName, const std::ve
             "-logsourcelocations",
             "-logtimemicros",
             "-logthreadnames",
-            "-loglevel=debug",
+            "-loglevel=trace",
             "-debug",
             "-debugexclude=libevent",
             "-debugexclude=leveldb",